The present invention relates generally to coal-fired primer movers driven by gaseous combustion products produced by the combustion of substantially dry coal particulates. More particularly, the present invention is directed to a coal-fired gas turbine engine or a reciprocating compression ignition engine in combination with an on-site coal preparing and supplying system capable of micro-pulverizing by coal particles and feeding the resulting micron-sized coal particulates into the combustion chamber of the selected engine.
The use of coal is of considerable interest as a replacement fuel for liquid and gaseous fuels such as fuel oil and natural gas for the firing gas turbines or compression ignition engines (Diesel). In coal-fueled gas turbine systems, fine coal particulates are supplied to the gas turbine combustor as a coal-water slurry rather than in the form of dry coal particulates since the pumping of such slurries, especially across a pressure barrier, is considerably easier to achieve with existing pumping systems than the pumping of dry coal particulates across and also reduces erosion problems associated with the pumping and valving systems in the fuel supply. By using such coal-water slurries, a relatively smooth combustion operation is achieved as compared to previously known arrangements for using dry coal as the fuel since relatively rapid changes in the flow rate of Combustion gases from the combustor to the turbine such as caused by several factors including the use of lock-hoppers which provide a pulse feed may result in turbine damage. Typically, the previously known fueling of gas turbines engines with coal-water slurries required that relatively large particles of coal be pulverized in a highly energy intensive mill to coal particulates of a size less than about 100 microns for combustion in the gas turbine combustor so that the ash and other products of combustion would be sufficiently small so as to provide minimal erosion problems in the turbine and combustion would be rapid. The coal particulates provided by the pulverizing mechanism are mixed with water at about a 1:1 ratio, by weight, so as to provide the coal-water slurry with an adequate pumping viscosity. Also, viscosity reducing and combustion stability increasing chemicals are frequently incorporated in coal-water slurries to enhance the combustion operation. This preparation of coal-water slurries for use in gas turbine engines is often provided at off-site locations and usually includes processes for removing sulfur and inorganic minerals normally found in coal. The resulting "clean" coal is then transported to storage tanks at the point of use by employing relatively expensive transportation modes such as tank trucks and the like. Thus, while the use of coal-water slurries in gas turbine systems provide many advantages over previously known uses of dry coal in such systems, there are still several shortcomings associated with the coal preparation, transportation, and handling of the coal at the engine site which detract from the use of coal-water slurries as a viable fuel in gas turbine applications.
The use of dry coal particulates as the fuel in internal combustion Diesel-type engines does not pose as many problems as previously found to be present with the use of coal in external combustion or gas turbines engines. Some success has been achieved by fumigating micro-pulverized coal particulates into the combustion chamber of Diesel-type engines with a stream of the combustion supporting air.
Mechanical milling mechanisms used to micro-pulverize the coal for use in the combustion chambers of the internal or external combustion engines consumes a considerable amount of energy. In using mechanical milling apparatus in manners as previously employed for appropriately micro-pulverizing the coal, whether in the form of bituminous, sub-bituminous, or lignite, consumes considerable energy with a substantial part of this energy being expended by increasing the temperature of the coal particulates during the milling operation. Much, if not all, of this thermal energy was not previously recoverable in the operation of the engine since in most systems the coal preparation was normally provided at off-site locations. This considerably expenditure of energy for the micro-pulverizing of coal and the lack of adequate recovery of this thermal energy also substantially detracted from the use of micro-pulverized coal in Diesel-type and gas turbine engines.